How to Configure SNMP?

Dear all,
I am very new to SNMP
.
Even though the question may seem to be silly,
I want your help!!!

My Questions are:

1.I am using BOSS linux 3.1(A Debian Derived Linux).
what is the use of SNMP?

2.If we want to monitor a system, is it required
to have SNMP to be installed ?

3.How to install SNMP and configure it?

4.How to find the version of SNMP installed in my system?

I tried to find with snmpwalk - It showed version like

SNMP V2- MIB

and executed tcpdump and it showed results like

ICMP request on

SNMP Version 1

Actually what is the version?

If we planned to use SNMPV3, what should be done???

5.How to enable SNMP port?

I was using Hyperic HQ open source monitoring tool which was installed on
System A.
I wished to monitor System B and I specified the IP address of System B to monitor in the Webbased tool in System A.
When I clicked Ok button , i got a message like,